[Preamble] Check system dependencies in preamble too

ilya-biryukov · ilya-biryukov · commit e5801b02e49b · 2018-07-09T09:07:01.000Z
Summary: PrecompiledPreamble hasn't checked if the system dependencies changed before. This resulted in invalid preamble not being rebuilt if headers that changed were found in -isystem include paths. This pattern is sometimes used to avoid showing warnings in third party code, so we want to correctly handle those cases. Tested in clangd, see the follow-up patch. Reviewers: sammccall, ioeric Reviewed By: sammccall Subscribers: omtcyfz, cfe-commits Differential Revision: https://reviews.llvm.org/D48946 llvm-svn: 336528
diff --git a/clang/lib/Frontend/PrecompiledPreamble.cpp b/clang/lib/Frontend/PrecompiledPreamble.cpp
@@ -63,6 +63,16 @@ createVFSOverlayForPreamblePCH(StringRef PCHFilename,
   return Overlay;
 }
 
+class PreambleDependencyCollector : public DependencyCollector {
+public:
+  // We want to collect all dependencies for correctness. Avoiding the real
+  // system dependencies (e.g. stl from /usr/lib) would probably be a good idea,
+  // but there is no way to distinguish between those and the ones that can be
+  // spuriously added by '-isystem' (e.g. to suppress warnings from those
+  // headers).
+  bool needSystemDependencies() override { return true; }
+};
+
 /// Keeps a track of files to be deleted in destructor.
 class TemporaryFiles {
 public:
@@ -311,7 +321,7 @@ llvm::ErrorOr<PrecompiledPreamble> PrecompiledPreamble::Build(
   Clang->setSourceManager(
       new SourceManager(Diagnostics, Clang->getFileManager()));
 
-  auto PreambleDepCollector = std::make_shared<DependencyCollector>();
+  auto PreambleDepCollector = std::make_shared<PreambleDependencyCollector>();
   Clang->addDependencyCollector(PreambleDepCollector);
 
   // Remap the main source file to the preamble buffer.
